1. Field of the Invention
The present invention relates to an optical write head for forming an electrostatic latent image on a photosensitive material by light emission elements disposed in rows.
2. Description of the Prior Art
FIG. 14 is a side view of a conventional electrostatic recording apparatus which has an optical write head 1 having light emission elements disposed in rows, for forming an electrostatic latent image on a photosensitive material 2.
The photosensitive material 2 is formed in layers on the circumference of a photoconductive drum 3 which, in turn, is rotatably connected to a drive device (not shown) for rotation in the direction of arrow 4. Around the circumference of the photoconductive drum 3, there are disposed a cleaner 6 for cleaning the surface of the photosensitive material 2, a charging corotron 7 for electrostatically charging the photosensitive material 2, the optical write head 1 for forming an electrostatic latent image composed of a plurality of exposed "dots" on the photosensitive material 2, a convergent lens 10, a development unit 8 for applying toner to the formed electrostatic latent dot image, and a transfer corotron 9 for transferring the toner-developed image onto recording paper 11.
The construction of a conventional optical write head is shown in FIGS. 15 and 16. FIG. 15 is a transverse sectional view of the conventional optical write head, and FIG. 16 is a fragmentary plan view thereof.
In FIG. 15, anode patterns 14 are formed within an evacuated, closed case 13 having a transparent separator 12. The anode patterns 14 are coated with fluorescing material at the upper surfaces of one end portion thereof. The fluorescing material is hereinafter referred to as "light emission elements" 15. A filament-like cathode electrode 16 is provided just under the transparent separator 12.
Cathode electrode 16 is heated by an electric current flowing therein, causing the emission of thermal electrons. When the cathode electrode 16 is grounded and a positive voltage is impressed on the anode electrodes 14, the thermal electrons collide with the light emission elements 15, causing them to fluoresce. As shown in FIG. 16, the anode electrodes 14 are arranged parallel to each other and are spaced at equal intervals but in an alternating relationship.
The plurality of anode electrodes 14 are electrically insulated from one another. A circuit is provided for selectively impressing a predetermined positive voltage individually to each anode electrode to provide a predetermined pattern. The light emission elements 15 emit light corresponding to the desired dot pattern to thereby form an electrostatic latent image on the photosensitive material 2 shown in FIG. 14.
Optical write heads designed as described above have been described, for example, in Japanese Patent Application (KOKI) Nos. 38967/83, 49249/84, 46740/83, etc. (the term "KOKI" as used herein means an "unexamined published application").
Such conventional optical write heads, however, have the disadvantage that the light emission elements must be arranged at regular intervals because the light emission elements are aligned in rows. The intervals are necessary for securing electrical insulation material between the spaced anode electrodes. For this reason, non-emission electrode portions exist between the light emission elements, thereby precluding improvement in dot density, and therefore image quality, beyond that achievable with the thinest insulation layer.
Moreover, such conventional optical write heads have another disadvantage in requiring as many drive elements as the number of light emission elements and a circuit having the capacity for controlling the light emission elements independently of each other. This requirement prevents significant reductions in the total cost of the apparatus.